Abstract
Abstract
Application of the theory of thermo-acoustic excitation of flames requires a detailed knowledge of the flame response to plane-wave velocity fluctuations of a given frequency through the burner. A model of the type of swirl burner used in some designs of industrial gas turbine is investigated, chemiluminescent emission being used as a marker of the hear release from both methane and propane premixed flames. The effects of the equivalence ratio and the withdrawal of the swirler so as to allow an annulus of unswirled premixture are also examined.
It is found that there are two distinct modes of self-excitation. The response of different burner configurations in the mode with the higher frequency is analysed in terms of four parameters. These characterize the position and spread of the axial distribution of heat release fluctuations, and the origin and effective velocity of convection of disturbances.
From these parameters, the Rayleigh integral can be calculated and this defines the frequency range over which excitation is possible. If the acoustic conditions require that the flame is lengthened, retracting the swirler, reducing the equivalence ratio or changing from propane to methane are all shown to be possible control measures for this particular burner.
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